Editorial Type:
Article
Article Type:
Research Article

Estimating Overwater Convective Boundary Layer Height from Routine Meteorological Measurements for Diffusion Applications at Sea

S. A. Hsu Coastal Studies Institute, Louisiana State University, Baton Rouge, Louisiana

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Print Publication:
01 Sep 1997
DOI:
https://doi.org/10.1175/1520-0450(1997)036<1245:EOCBLH>2.0.CO;2
Page(s):
1245–1248
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Abstract

On the basis of hourly measurements of wind and air and sea surface temperatures for at least 6 yr at three buoy stations in the eastern Gulf of Mexico, the onset of the free convection regime, which coincides with the commencement of stability class C (for slightly unstable conditions in the Pasquill stability classification) at approximately Rb = −0.03, −Z/L = 0.4, and −Zi/L = 5, is verified over the ocean, where Rb is the bulk Richardson number, Z (= 10 m) is the height above the sea, L is the Monin–Obukhov stability length, and Zi is the height of the convective boundary layer (CBL). Datasets for the CBL are analyzed in the context of the boundary layer physics of Garratt. It is found that Zi is linearly proportional to the surface buoyancy flux—that is, (w′θ′υ)0, where w is the vertical velocity and θυ is the virtual potential temperature. For operational diffusion applications, a statistical formula is proposed—that is, Zi = 369 + 6004(w′θ′υ)0. A method to compute this buoyancy flux from routine meteorological measurements is also provided.

Corresponding author address: Dr. S. A. Hsu, Coastal Studies Institute, Louisiana State University, 308 Howe/Russell Geoscience Complex, Baton Rouge, LA 70803-7527.

sahsu@antares.csi.lsu.edu

Abstract

On the basis of hourly measurements of wind and air and sea surface temperatures for at least 6 yr at three buoy stations in the eastern Gulf of Mexico, the onset of the free convection regime, which coincides with the commencement of stability class C (for slightly unstable conditions in the Pasquill stability classification) at approximately Rb = −0.03, −Z/L = 0.4, and −Zi/L = 5, is verified over the ocean, where Rb is the bulk Richardson number, Z (= 10 m) is the height above the sea, L is the Monin–Obukhov stability length, and Zi is the height of the convective boundary layer (CBL). Datasets for the CBL are analyzed in the context of the boundary layer physics of Garratt. It is found that Zi is linearly proportional to the surface buoyancy flux—that is, (w′θ′υ)0, where w is the vertical velocity and θυ is the virtual potential temperature. For operational diffusion applications, a statistical formula is proposed—that is, Zi = 369 + 6004(w′θ′υ)0. A method to compute this buoyancy flux from routine meteorological measurements is also provided.

Corresponding author address: Dr. S. A. Hsu, Coastal Studies Institute, Louisiana State University, 308 Howe/Russell Geoscience Complex, Baton Rouge, LA 70803-7527.

sahsu@antares.csi.lsu.edu

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Cover Journal of Applied Meteorology and Climatology
Journal of Applied Meteorology and Climatology

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